1. Field of the Invention
The invention relates to a fan blade shaped to reduce noise during operation thereof.
2. Description of the Prior Art
A typical fan assembly for the application of condenser cooling in both residential and commercial air conditioning systems consists of a hub, a multi-wing spider, and multi blades, which could be 2, 3, or 4 blades. Each spider wing is attached with a blade through riveting or spot welding or other mechanical means. In a typical condenser cooling application, the fan is directly driven by a motor to draw airflow through the condenser coils to achieve cooling effect. The current art of condenser fan assembly implements rectangular blade shapes. These fans will generate sufficient air to meet varied cooling needs when they are pitched properly, however, they also radiate high levels of noise during operation.
In a typical condenser cooling application, the upstream air flow of a rotating fan is partially distorted due to the blockage of compressor, controlling panels, etc. As a result of it, tonal and broadband noise will be generated by a rotating blade leading edge cutting through the flow distortion, i.e. turbulence. Each small segment of the leading edge along the radial direction acts as a noise radiator.
It is an object of the invention to provide a unique and effective blade for a fan assembly which produces sufficient air for cooling purposes with low noise level.
The fan blade is formed from a flat blank bent to a desired shape to form the fan blade. The fan blade has a front side, a rear side, an inner attachment portion, an outer edge, a curved leading edge and a curved trailing edge. The outer edge defines an arc between a forward position and a rearward position. The leading edge extends outward and intercepts the arc of the outer edge at the forward position and the trailing edge extends outward to the rearward position. An angle xcex1L is formed by a straight line having a length equal to RL extending from a given axis coinciding with the axis of the fan to the forward position and a line extending from said given axis to a first position on the leading edge and having a length equal to about 0.5RL wherein the angle xcex1L is equal to at least 35 degrees.
In a another aspect, the ratio of HL/LL is larger than about 0.10 but less than about 0.20, wherein LL is the length of a straight line from the first position to the forward position and HL is the maximum distance from LL to the leading edge as measured from a straight line perpendicular to LL and extending to the leading edge.
In a further aspect the angle xcex1T is at least 30 degrees but less than 40 degrees wherein xcex1T is formed by a line having a length equal to RT extending from said given axis to the rearward position and a line extending from said given axis to a second position the trailing edge and having a length equal to about 0.5RT.
In addition, the ratio HT/LT is larger than about 0.10 but less than 0.20, wherein LT is equal to the length of a straight line from the second position to the rearward position and HT is equal to the maximum distance from LT to the trailing edge as measured from a straight line perpendicular to LT and extending to the trailing edge.